The word “ substitution " means that to use something new or different instead of something else. Also, it can use in math,too. For example, I have two slope intercept form
y-2x=6
-y-4x=24
Now, we just need to substitute the two of them to find x and y
-y-4x=24 + y-2x=6 = -6x=30 x=-5 Then, replace variable if x in one of them to find y
y-2x=6 y-2(-5)=6 y+10=6 y=6-10 y=-4. Hope it help!